Add a seed to the gru unit test
Add a seed to the gru unit test

Summary:
as it calls np.random and sometimes fails unreproducibly
Closes https://github.com/caffe2/caffe2/pull/1779

Reviewed By: pietern

Differential Revision: D6779802

Pulled By: anderspapitto

fbshipit-source-id: 2ad069f8a15f70a8110b1a6bdb06f81577c53ad4

xzturn/caffe2,caffe2/caffe2,xzturn/caffe2,Yangqing/caffe2,Yangqing/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2